Small, inexpensive, cameras for use with computers are commonplace. These cameras are constructed from an imaging array and a lens that is set at a fixed distance from the imaging array. The lens position is normally set during the final stages of production. Typically, the position of the lens relative to the imaging array is measured after the camera is assembled. The lens is then moved to the correct position by turning the lens in a screw mount a fixed number of turns to bring the lens-imaging array distance to the correct value. Once the position of the lens is set, the lens is immobilized so that the distance from the lens to the imaging array cannot be changed.
The cost and accuracy of this adjustment depends on being able to rotate the lens a known angular distance. If the device that moves the lens is inaccurate or has backlash, or slips, the final positioning will be inaccurate and the product will not function properly. This will be reflected in a lower device yield and higher device prices.